Mine shafts are created in the process of tunneling underground in order to extract mineral resources. Once a desired mineral resource has been extracted from a shaft, the shaft may no longer be used for further mining. Shafts are also sometimes abandoned for commercial reasons, such as when the company operating a mine ceases operations. Mine shafts which are no longer in use may be sealed for any of a number of reasons, for example to reduce subsidence or to reduce safety and health hazards caused by the emission of gases within a shaft.
Mine seals are generally required by regulations to meet certain standards of strength and resistance, in particular resistance to explosive force and static load. Under rules announced by the Mine Safety and Health Administration in 2008, new mine seals are required to withstand pressures of at least 50 pounds per square inch when the atmosphere inside a sealed area is monitored and maintained without explosive methane concentrations, while seals in areas that are not being monitored or maintained inert must withstand pressures of at least 120 pounds per square inch. In areas where explosive methane concentrations are likely or conditions such as bottom mining might increase blast forces, seals must be designed to withstand pressures of more than 120 pounds per square inch.
Current mine seals are generally formed by cementing concrete blocks in place to form a wall at the entrance to a shaft, a process that typically requires several days and involves transporting quantities of water and cement into a mine in order to create mortar on-site. While concrete blocks can generally resist upwards of 400 psi of compressive force, the mortar portion of the mine seal is less resistant. A need therefore exists for mine seals having improved structural properties which can be formed in the environment of an underground mine.